The present invention relates to a method for estimating the origin time, the hypocentral distance, and the scale of an earthquake from time-series data of measured values of the electric field intensity which is observed accompanying the seismic ground motion, and to an apparatus for the prediction.
In the prior art, the origin time, the hypocentral distance, and the scale of an earthquake are calculated based on the measurements of only P wave, or both P wave and S wave. It is necessary for calculation of these values to measure P wave of the same earthquake at four or more observation sites, when P wave only is used. Even when both P wave and S wave are used, it is necessary to measure P wave and S wave of the same earthquake at three or more observation sites.
For example, in case the hypocentral distances of the four p wave observation sites are 100 km or shorter, the calculation of the origin time (time of earthquake occurrence), the hypocentral distances (distance from the hypocenter to the observation sites), and the scale (magnitude M) requires at least 15 seconds, which is a time P wave requires to arrive at the observation sites. However, as a typical observation uses both P wave and S wave, the calculation requires at least 25 seconds, which is a time S wave requires to arrive at the observation sites in case the hypocentral distances of the three observation sites are 100 km or shorter. No matter which method is used, the hypocentral distance and the scale can not be known until seismic waves arrive at three or four observation sites, that is, for 15 or 25 seconds after the occurrence of the earthquake in the above described cases.